NRC Ratings for Eggcrate Foam

Noise Reduction Coefficient (NRC)

Acoustical foam's effectiveness is measured by its Noise Reduction Coefficient, or NRC rating. The NRC of a material can be found by using either the Reverberation Room Method (ASTM C423) or the Impedance Tube Method (ASTM C384). We use the Reverberation Room Method. 1) Approximately 72 square feet of material is rested on the floor of a reverberation chamber. This chamber usually has all hard concrete surfaces. 2) The change in absorption from the room without material compared to the room with material is measured. 3) The changes in sound are measured for octave bands ranging from 125Hz to 4000Hz, recording the differences in Sabin absorption coefficients. The overall NRC rating is the calculated average of frequencies 250Hz, 500Hz, 1000Hz, and 2000Hz, which is then rounded to the nearest multiple of 0.05.